|P is for Practical|
You are right that metaphors are usually not illegal in themselves. But if you get into trouble, they can make your trouble much worse. Your state of mind when you commit a crime often determines which crime you will be charged with. Military metaphors can be a worst-case-scenario for your defense.
For an example, see http://www.smartmoney.com/onthestreet/index.cfm?story=20040630&pgnum=3. In this article, it is clear that the state of mind of the enery traders determines whether or not a crime occured. If I was on a jury, and someone claimed to be in an innocent state of mind while executing manuever that they themselves referred to as 'Death Star', I would be skeptical.
If you aren't accused of commiting any crimes that relate to your metaphors, there should be no legal problems with choice of metaphors. However, many military tactics are in fact illegal when applied to civilian life. Shooting at your competitors, for example, is generally forbidden.
Perhaps it would help to shift metaphors to illustrate the point with a silly example. I'm not being serious, here, I'm just trying to explain my point of view. If you don't agree or think it applies, that's fine, too. People who debate crime, punishment, and metaphor often don't agree.
Imagine that I am an accountant. I unwisely call my tax-avoidance system "Fraudulently avoid paying taxes by illegally deducting business lunches." During an audit of an account which uses this scheme, it is found that I should not have deducted an expensive business lunch that was listed as an expense. Now it is the Revenue Agent's responsibility to assess my state of mind when I made this mistake. Was it tax evasion, or a simple mistake? The name of my accounting scheme is going to cause me a problem.
Not silly enough? Here's one that's even sillier: What if Scott Adams was charged with stealing office supplies? As the author of "Build A Better Life By Stealing Office Supplies" he could have a real problem!
There is also a more serious risk in using metaphor, and that is that an opponent takes your metaphor literally, and shoots first. The Salvation Army doesn't have much of a problem with that one, but Mall Cops do take that risk, and sometimes pay the ultimate price.
It should work perfectly the first time! - toma